VARIABLE STROKE PISTON MECHANISM FOR SPARK-IGNITION ENGINES

The concept of load control in internal combustion engines by eliminating the inlet throttle and replacing it by controlling the piston stroke has gained great publicity recently. Nevertheless, certain design parameters should be considered in order to make this concept worthwhile. In this study, an optimized mechanism for varying engine stroke has been introduced. A criterion based upon the use of complex numbers technique was used to analyse the mechanism kinematically and dynamically and the results were then verified using graphical solution. The mechanism was found to produce up to 56% stroke variation within the control actuator capabilities. The compression ratio was found unchanged (within +/- 6%) which helps maintain steady combustion process. The entire mechanism is well tuned and no spark plug timing adjustment is required during stroke variation. The piston side thrust due to connecting rod angularities was found to be fairly low and should not impose any wear problems in the engine cylinder walls.